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    <title>Document</title>
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    <script>
    // 输入：[1, 2, 3, 4], ['a', 'b', 'c', 1]
    // 输出：[1, 2, 3, 4, 'a', 'b', 'c', 1]
      let arr1 = [1, 2, 3, 4];
      let arr2 = ["a", "b", "c", 1];
      let arr3;

      function concat(arr1, arr2) {
      
        arr3 = [...arr1, ...arr2];
      }
      concat(arr1, arr2);
      console.log(arr3);
    </script>
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